1. Field
The present disclosure relates to a system and a method for enabling halftoning of a color image based on its color separation content.
2. Description of Related Art
For raster type color image printing systems, which have been implemented with various print engines such as electrostatographic print engines and ink jet print engines, Page Description language (PDL) pages or other input pages or sheets are Raster Image Processed (RIPed) to a continuous tone image data (or contone compressed format).
Raster type color image printing systems commonly employ halftoning to transform the continuous tone (contone) image data to print data that is printed as an array of dots that are of substantially similar size. For example, 8 bits per pixel per primary continuous tone (contone) image data is halftoned to one-bit data per pixel per primary color. Halftoning is traditionally performed on a print engine of the image printing system for color adjustment reasons. Halftoning may occur on a Digital Front End (DFE) of the image printing system.
In printing color documents, obtaining the desired density of a particular color is accomplished by halftoning, where separation density variation is represented by marking greater or fewer numbers of ON pixels (binary) in a distinct area of a separation. In a halftoning method known as dithering, or screening or halftoning, a value representing the density of each color separation pixel of an array of separation pixels within the area is compared to one of a set of preselected thresholds (i.e., stored as a dither matrix or halftone screen). The effect of such an arrangement is that for an area where the image density of the color separation lies between the maximum and minimum levels, some of the thresholds within the dither matrix will be exceeded while others will not. In the binary case, the separation pixels for which the thresholds are exceeded might be printed as a maximum colorant value, while the remaining separation pixels are allowed to remain white, dependent on the actual physical quantity described by the data.
While widely accepted as a method for rendering color prints of digital images, halftoning and the resulting halftone dot pattern may sometimes create image quality problems. For instance, when a halftone dot pattern is used to render edges in text and other objects with fine detail, the halftone structure may cause edge raggedness. Also, when halftone color separations are superimposed over other halftone color separations in a multiple color separation image, moire and other pattern artifacts may occur. Reduction of pattern artifacts consumes a great deal of effort when designing halftone screens for a printer or other image output device. Much effort has been spent on techniques to avoid pattern artifacts when printing multiple separation color halftones; however, some undesirable patterns still remain and may be found in commonly printed material.
On the digital image printing systems, customer selected halftone dots use the same dot angle and frequency without any analysis of the page/object/job separation content. Most conventional halftoning assumes that four colors (colorants) will be printed and halftone screens are selected accordingly. A downside of such an algorithm is that printed output for single or dual separation content may be grainy or noisy and the dot may be more noticeable due to sub-optimal dot angle design as opposed to a dot designed for the single or dual separation content.
Therefore, it would be desirable to have a halftone screen selection process that could be performed within an image path (i.e., automatically) and localized to color separation content within a color image.